1. Field of the Invention
The present invention relates to a superabsorbent polymer herbidical delivery agent having excellent formulation flexibility, controlled release potential, run-off resistance and hydrodynamic properties.
2. Description of the Prior Art
Infestations of aquatic and wetland plants (weeds) such as hydrilla, southern water-grass, waterhyacinth, watermilfoil, Salvinia etc., have caused detrimental effects on health, agriculture, commerce, and recreation in many areas of the United States and overseas. When present in high densities, these weeds can literally choke lakes and rivers, thereby preventing access by boats and barges. In addition, these weeds can disrupt the functioning of drainage, irrigation, flood control and water conservation projects and hydroelectric power plants, provide breeding grounds for disease carrying mosquitoes and snails, eliminate fishing in certain areas, and alter aquatic ecosystems by preventing sunlight from reaching other plants and animals which live beneath these vegetative mats. Therefore, the growth of these nuisance plant populations must be controlled.
Aquatic and wetland weeds can be controlled by heavy machines (mechanical control) by a variety of insects, pathogens, and other organisms (biological control) by drawdowns, plastic sheets, and colored dyes (cultural control), and, most commonly, by the use of chemical herbicides (chemical control). The concurrent or sequential use of two or more of these control procedures is referred to as integrated control. Solid and liquid herbicide formulations designed for quick and slow or controlled release of the active ingredients are currently in use to control aquatic and wetland plants; however, new formulations are needed that can enhance the efficacy and/or extend the range of performance of existing products.
U.S. Pat. Nos. 4,400,391 and 4,401,456 disclose the use of alginate gel beads to encapsulate bioactive materials to provide for their controlled release. The patent describe beads being made to either float or sink (if used in an aqueous environment) and they may contain herbicides. These beads are also described as acting as carriers to place the bioactive material near the target species, for example, a floating bead containing a herbicide releasing the herbicide in close proximity to floating aquatic weeds, or the beads falling through foliage to release herbicide into the soil. U.S. Pat. No. 4,344,857 involves encapsulation of xanthate derivatives. The encapsulation techniques are complicated, costly and quality sensitive.
A relatively new approach to herbicidal delivery has been by application of controlled release formulation such as described by Richard W. Baker in Controlled Release of Biologically Active Agents, 1987, Wiley-Interscience Publishing, 279 pp. This book describes the use of various controlled release technologies including simple diffusion from monolithic devices such as hydrogels. More complex release mechanism include the use of biodegradable matrix carriers, bonding of active ingredients in heterogeneously or homogeneously degradable polymers, called polyagents. Polyagents may actually be polymers formed of monomers of the active agent. The release mechanics of these controlled release mechanisms are complex depending on the presence (and strength) or absence, of degradable ligand bonds and their location of the degradable bonds (e.g., as active agent bonds to the polymer), the concentration of the active agent and/or dispersant or solvent in the carrier, the relative hydrophobicity or hydrophilicity of the polymer, whether or not the polymer degrades homogeneously or heterogeneously, whether the active agent is in the solid form or the liquid form in the polymer, etc.
A relatively new class of polymers has recently been introduced that exhibits remarkable absorbency. However, there has been no recognition of their uses for herbicidal delivery. One example is the acrylic-based superabsorbent polymers The aqueous absorbency mechanism of acrylic-based superabsorbent polymers has been described by the Chemdal Corporation (Arlington Heights, Ill. 60004) in their Technical Data Sheets on Aridall.RTM. Superabsorbent Polymers. The absorbency of acrylic-based superabsorbent polymers is attributed to the carboxylic groups located on the backbone of the superabsorbent polymer. When water contacts their superabsorbent polymer, these groups solvate rapidly and develop mutually repulsive negative charges. This causes the superabsorbent polymer to uncoil and absorb many times its weight in water. Crosslinking prevents solution of the superabsorbent polymer. The aqueous medium rapidly becomes oriented on the surface of the superabsorbent polymer by virtue of hydrogen bonding. The resulting gel has remarkable ability to hold the aqueous medium even under pressure. Superabsorbent polymers hold fluids by a physico-chemical mechanism. Electrolytes/salts interfere somewhat with the hydrogen bonding. Crosslinked acrylic-based superabsorbent polymers always absorb less aqueous medium when electrolytes/salts are present.